Oil and gas well treatments are notorious for unexpected results. What may increase production in one well may shut off another well. Yet a successful well treatment can significantly increase production of a well and extend its production life, with rapid economic payback of the cost of the well treatment. Significant research is therefore devoted to improving well treatments.
One such common well treatment is the fracturing of a well formation using various load fluids and proppants to increase formation permeability, commonly known as a frac. Pressure on load fluid in the well causes cracks to form in the formation and proppants (sand, for example) injected into the well with the load fluids become wedged in the cracks, thus keeping the cracks open and increasing permeability. Various load fluids are used for fracturing, including oils, water, methanol and other alcohols, carbon dioxide, explosives, and acids.
In Canadian patent no. 1,268,325 of Mzik there is described a method of treating a well formation penetrated by a wellbore which comprises injecting down the wellbore and into the formation a fluid mixture comprising a mixture of carbon dioxide and a hydrocarbon fluid containing aromatics at a pressure sufficient to cause fracturing of the formation.
It has been found that fracturing a well with a mixture of carbon dioxide and hydrocarbon fluid containing aromatics yields variable recovery of load fluid in the general case, and thus an uncertain economic return from the use of the method. Low recovery of load fluid may cause a reduction in permeability of the formation, with consequent decline in production from the well. Hence, the economic efficiency of application of the method of Mzik to an oil or gas well is somewhat uncertain, and may in fact be deleterious to the well productivity. Yet the use of carbon dioxide and a hydrocarbon fluid containing aromatics may provide significant economic benefits as shown by the example in the patent of Mzik.